Many grades of coal and petroleum contain large quantities of sulfur compounds which form corrosive air and water pollutant products during combustion. A number of chemical and physical processes have been developed to remove inorganic sulfur contaminants, such as sulfates and iron pyrites. Some organic sulfur compounds, such as mercaptans, aliphatic sulfides and disulfides are relatively amenable to chemical removal. However, the aromatic sulfur compounds, such as diphenylsulfide, benzothiophene, dibenzothiophene and the like, are found in predominating concentrations in coal. These sulfur compounds are resistant to chemical and microbial attack and are frequently characterized as refractory organosulfur compounds.
A number of chemical processes for removal of organic sulfur are under investigation. Among the processes being evaluated on a laboratory or pilot scale are oxydesulfurization, chlorinolysis, oxidation, hydrodesulfurization and Gravimelt. According to Berry [Berry, R. I. (1981), "Guide to Coal-Cleaning Methods," Chemical Engineering, January 26], projected total product costs from bench and pilot scale operations ranged from $41 to $58 per ton (in 1979 dollars) for 10 to 50% organic sulfur removal.
Removal of such refractory organic sulfur compounds by microbial treatment would have many important advantages. Since high temperature, high pressure or corrosion resistant equipment are not required for the biological process, inexpensive construction materials can be used leading to low capital costs. Processing costs can also be low if waste materials are utilized to support the microbial growth. Biological treatment can be carried out under ambient conditions in many locales. Microbial treatment is not likely to significantly alter the structure and composition of the coal or to substantially reduce the BTU value of the coal.
Microbiological treatment of petroleum and coal has been under experimental investigation utilizing a variety of microorganisms, including genera such as Pseudomonas, Alcaligenes, Bacillus, Desulfovibrio, Thiobacillus, Arthrobacter, Flavobacterium, Beijerinckia, Rhizobium, and Acinetobacter. Some of these microorganisms showed potential for degrading refractory organic sulfur compounds as discussed by Hedrick et al. [Hedrick et al (1982), "Desulfurization of Coal by Biological Pretreatment," State-of-the-Art]. This article provides a comprehensive summary of such experimental efforts. However, neither this report nor other available art discloses the mutant microorganism Pseudomonas sp. CB1 (ATCC #39381) or its efficacy in removing sulfur from refractory organic sulfur compounds, such as the thiophenes found in carbonaceous materials.